Smacking is just another word for hitting.

Is there a difference between slapping and hitting?

Slap means to strike with the open hand. Hit and beat are both synonyms, they are both generic terms for strike, but often are used to mean with a fist.

What is the difference between spanking and smacking?

Whereas a spanking is invariably administered to the bottom, a "smacking" is less specific and may refer to slapping the child's hands, arms or legs as well as its bottom.